The sheet panels having folded borders are used extensively in the construction of electro-domestic articles, boxes, furniture and metallic shelving. The production of these articles is carried out with suitable folding machines the main features of which are a system of blades and a blank holder device by means of which it is possible to produce the desired fold on the flat sheets which are subjected to the action of the folding machine.
It is part of the known technology with respect to folding machines to use a pair of blades opposed one to the other supported by a cutter block in the shape of a "C" which is movable in the vertical direction with respect to the blank holder device. This blank holder, in the case of the production of panels which have the borders folded towards the interior, must be capable of contracting in order to allow the motion of the same panel. In addition, there must be the possibility of varying the extension of the same blank holder in a manner to be able to change rapidly the dimension of the panels which are produced and the profile of the fold of the same panels.
It is also part of the technology of the folding machines to provide for the modification of the length of the blank holder device in a programmed manner. The variation of the length of the base of the blank holder is achieved in the folding machines already known in the art by varying the number of suitable segments of which the blank holder itself is composed. The final regulation of the length of the blank holder is then achieved by substituting the members at the extremities of the blank holder. On the side of the blank holder, the folding machine in addition must provide for the presence of two storehouses which contain a plurality of corresponding symmetrical members at the extremities and also suitable means for their automatic and programmed substitution. The latter may consist for instance of programmer carriages provided with suitable separation systems which are slidable along suitable guides due to the rotation of screws which are as long as said guides and which are moved in two directions by suitable motors.
The motion of the carriages which are used to achieve the substitution of the extremity members must be simultaneous and suitably synchronized with the contraction phase of the same blank holder.
This type of configuration which is used with the folding machines known at present is affected by several functional limitations due to their complexity, limitations which cause mechanical problems which increase the cost of management and upkeep of the same folding machines. The considerable dimensions and consequently the space involved is another problem of the type of folding machines known at the present.
In conclusion, the limitations of the known folding machines are:
1) The presence of two storehouses which contain a corresponding plurality of tools, a fact which causes cost increases and a substantial space requirement; PA1 2) Excessive machinery involved in the system of hooking and unhooking of the members which are used at the extremities, with mechanical problems and increase in the upkeep cost; PA1 3) The necessity of carrying out the change of the extremity members only in a certain vertical position of the blank holder with respect to the front plate of the folding machine which is vertically fixed.